In fact, the report mentions that birds have lost their teeth at least 4 times according to fossil records. The traditional theory according to the author, Chiappe, is that teeth are heavy so birds evolved beaks which are lighter.
MORE: http://scienceblogs.com/lifelines/2013/01/08/ancient-bird-had-specialized-teeth/
See also...
We're closer to learning how songbirds make those sounds
http://www.msnbc.msn.com/id/50403635/ns/technology_and_science-science/
